Apparatus exists for measuring the roughness of surfaces such as roads and highways, by means of propelling a suitable vehicle over the surface. The vehicle carries equipment which physically contacts the surface to determine roughness which is then displayed in a suitable manner. One such device is described in U.S. Pat. No. 3,459,038 issued Aug. 5, 1969, to G. Swift. Another device is described in U.S. Pat. No. 3,888,116, issued June 10, 1975 to J. R. Nims.
Mechanical road-contacting devices have the disadvantage of being very sensitive to the suspension of the vehicle under which they are mounted: the vertical component of motion frequently greatly impairs the accuracy of the surface-roughness measurement. For some surfaces, e.g. water, contacting probes are not practical. Thus, a remotely-operated system (one in which no physical contact is made to the surface) is of advantage.
Doppler radars for measuring vehicle speed are known. The radar transmitter-receiver antenna is usually mounted at an angle to the surface over which the vehicle travels. Reflected signals from the surface are mixed with the transmitted signals to produce the difference frequency, which is indicative of speed as is known to those skilled in the art. The radar receiver also detects frequencies not of interest in detecting speed, which are unavoidable and undesirable and usually filtered out in the speed measuring apparatus. One such speed measuring device is described by H. C. Johnson in "Speed Sensors for Locomotives," RCA Engineer, August-September 1976, pp. 34-37.